Hi, Tracy!
For me and my family, we usually choose one Port Adventure which really appeals to us, and then, we explore (like you mentioned) for another. We have a family of six. Therefore, Port Adventures can add up quickly for us in multiple ports. For the Western Caribbean, you have the benefit of several ports of call -- Key West, Grand Cayman, Cozumel and Castaway Cay.
My recommendation is to plan a Port Adventure in Cozumel which allows you to see the ruins and enjoy the landscape of this adventurous port, and then if your vacation budget allows, book a Port Adventure in Grand Cayman like the
Nautilus Undersea Tour. It's moderately priced and only takes two hours. You can feel like you've experienced something unique to that area by seeing what the scuba divers see. Plus, you'll have more time to explore the small island, spend some time at the beach or go shopping. Remember that this is a tendered port and allow time in your schedule for getting back and forth to the ship.
Have a wonderful day and a magical vacation. Bon voyage!
Andi